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Re: UUID in fstab for device mapper devices?

On Mon, Aug 10, 2009 at 12:20:30PM +0200, Ferenc Wagner wrote:
> Guido Günther <agx@sigxcpu.org> writes:
> > On Sun, Aug 09, 2009 at 09:31:48PM +0200, Ferenc Wagner wrote:
> >
> >> Guido Günther <agx@sigxcpu.org> writes:
> >> 
> >>> Dropping user_friendly_names won't give you name persistence with
> >>> and without mp all by itself. You'll either have to use disk/by-id
> >>> or disk/by-uuid to achive that.
> >> 
> >> Why not?  The WWIDs, which are used to name the devices by default,
> >> are persistent and also consistent between machines, aren't they?
> >
> > Yes, these are persistent across machines but they aren't persistent
> > as to switching multipath on and off (see below).
> Hi Guido,
> Thanks, I got your point now.
> > We could have the same fstab with and without multipath. This would
> > be convenient for our users since they'd have easier means of error
> > recovery (and an easy way to turn multipath on and off):
> And to run without multipath without noticing until the first path
> failure.
> > Without multipath:
> > /dev/disk/by-uuid/<UUID> -> /dev/sdaY 
> >
> > With multipath:
> > /dev/disk/by-uuid/<UUID> -> /dev/mapper/<WWID>-partY
> Multipath is critical enough in my systems that I prefer explicit
> control and early failure dealing with it.  Others may have different
> preferences, of course.
I see your point. Maybe we can even have both /dev/mapper/<wwid> as well
as /dev/disk/by-uuid/ support in d-i. This would be even simpler if d-i
would use /dev/disk/by-uuid instead of UUID= by default. Is there any
good reason not to do this? Udevless systems?

> Also, how does this carry over to multipathed root?  I'd guess
> initramfs needs the real device name after root= anyway, doesn't it?
Haven't checked but shouldn't a /dev/disk/by-id/ path also work. We have
all the stuff up in the initramfs already.

> >> To get really friendly names, I define aliases in multipath.conf,
> >> but that's mostly sugar, I could do without them.  Losing name
> >> consistency amongst different machines would be a major
> >> inconvenience, though.
> >
> > I wouldn't object getting rid of user_friendly_names in
> > multipath.conf, but preferably by switching to /dev/disk/by-{uu,}id
> > then.
> I'd welcome that.  It may not be the exact thing I'd want, but good
> enough to start from.  I may as well get to love it in the end. :)
Now we only need somebody to work on that ;) Seriously: I won't be able
to spend much time working on it in the near future but at least we have
a direction where we should be heading.
 -- Guido

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